Update comments as requested by code review.

Author: dpvc

ts/core/MmlTree/MmlNode.ts

@@ -351,6 +351,8 @@ export abstract class AbstractMmlNode extends AbstractNode implements MmlNode {
    * @override
    *
    * @param {boolean} keepIds   True to copy id attributes, false to skip them.
+   *                              (May cause error in the future, since not part of the interface.)
+   * @return {AbstractMmlNode}  The copied node tree.
    */
   public copy(keepIds: boolean = false): AbstractMmlNode {
     const node = this.factory.create(this.kind) as AbstractMmlNode;

ts/core/Tree/Node.ts

@@ -276,7 +276,9 @@ export abstract class AbstractNode implements Node {
     const node = (this as AbstractNode).factory.create(this.kind) as AbstractNode;
     node.properties = {...this.properties};
     for (const child of this.childNodes || []) {
-      if (child) node.appendChild(child.copy());
+      if (child) {
+        node.appendChild(child.copy());
+      }
     }
     return node;
   }

ts/input/tex/cases/CasesConfiguration.ts

@@ -11,7 +11,7 @@ import {MmlMtable} from '../../../core/MmlTree/MmlNodes/mtable.js';
 import {EmpheqUtil} from '../empheq/EmpheqUtil.js';
 
 /**
- * The StakItem for the numcases environment.
+ * The StackItem for the numcases environment.
  */
 export class CasesBeginItem extends BeginItem {
 

ts/input/tex/empheq/EmpheqUtil.ts

@@ -35,7 +35,7 @@ import {EmpheqBeginItem} from './EmpheqConfiguration.js';
 export const EmpheqUtil = {
 
   /**
-   * Create the needed envonronment and process it by the give function.
+   * Create the needed envinronment and process it by the give function.
    *
    * @param {TexParser} parser   The active tex parser.
    * @param {string} env         The environment to create.